Telephone system



June 2, 1925. 1,540,043

H. s. TURNERw TELEPHONE SYSTEM Original Filed Feb. 27, 1915 2 Sheen s-Sheet 1 v lnvenfor: I Hubert S. Turner June 2, 925 1,540,043 H. 5. TURNER 4 TELEPHONE SYSTEM Original Filed Feb. 27, 1915 2 set 2 f/y a 5: J50

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rl'l l l'l lgiglg;

3/3 I 3/2 F1946 298 /n venfor:

Patented June 2, 1925.

cry 27, 1915, Pu

T STATES" PATENT -otsicsz.

EUBERT"S. TURNER, 02E BROOKLYN, NEW YORK.

TELEPHONE SYSTEIYE;

Originalepplicationmen .lfebruery 27, 1915, Serial No. 11;,046. iltvided andthis duplication filed February 6, 1923.

which connections betweensubscribers linesure established by means of cord end trunk.

circui This application u division of application,Serntl No. 11,046, ti led Fel ru-. tent No. l,4l-,5l,896, April 17,

In telephone systems Where connections between subscribers .lineserc established by means of .operotors 'COL'ClitIKl: trunk circuits, :1. calling" su-l isci-iber, hzrvi-ng initiated a cell, may hung up his receiver before the called criber answers, either due to the failure the culiled subscriber to answer quickly enough, or due to the abandonment oi the (will, by the culling subscriber. In such acese where :1 cell is ubzmdoned, it is unnecessary to continue the ringing of the called subseribefis line. 1

H retol ore insysi-ein-sot this nnture,itIthe opei orut the Aer-answering switchboard, or the operator at the Ber trunk switch board is slow in taking down the' connection in the case of an ,ebu-ndoned call, ring; inp; current would continue to flow over the culled-for line and this line Would be inacccssible other incoming calls until the connection had been taken :down, and the called subscriber may be delayed in extending; :1 call from his station.

One of the objects of this invention is, therefore, to enable the callingsubscriber to control the disconnection of the rinuchinc ringing iron the called line in systems where Hie-connection between the cullingnnd'called lines is built up over at cord and a trunk cir-' The above and other objects are obtained smear No. 617,239.

according to one feature of this invention by the provision of; cord and trunk circuits wherein u ringing. relay is deenergizedby the replacement of the receiver on the SWltC'lk, hook et it calling substation .toeutomatically disconnect a ringing. current source from the,

cord circuit thereby discontinuing the How of ringing current over the called line.

Another feature of this, invention resides in the nrrwisicn 0.1 trunk aielays, which are controlled bythe atoreseidringing relay and which in turn control the cut-oft relay oIf-u col-led line so that when n .crtl'ling subscriber restores the receiver to the switchhooli, the deeuergization of the ringingreley effected thereby, causes the deenergizetion oi the trunk and cut-oil relays thereby restoring the line signal of the called line toajthe control of the called subscriber and removing the busy potential from nuiltiple jacks, as-

sociated with the line. I

The invention will be readily understood from the following detailed description and by reference to the accompanying drawing, in whichl ig. 1 showse subscribers line and. an operetofls cord circuit embodying features of this irwention; 2 shoiirsthe u'iezins employed in nilzilting busy tests; Fi 41: and 5 show three different forms 7 trunk circuits whichelnbody features of this invention and are adepted'to cooperate with the cordcircuit shown in Fig- .1' in completing connections between calling and celledv subscribers, Fig. 6 Shows on alternate form of ulportion oi? the modification shown in Fina 5. I

Referring; first to Fig. 1, 1 represents 21 telephone substation Which includes a tele phone receiver 2', a transmitter 3., a. switch.

boo; 4;, cull hell 5, ,ztcondenser 6,, and primary 7 and secondary S of an induction coil. The elements 3 and 7 ere included in a bridge of the telephone line, which is open when the telephone receiver is. upon the switchhooli 4 end which is. closed by the switchhook 4'. when relieved of the W r nht of he telephone receiver. 'lheclements and Gore included in another bridge perinencntly continuous with respect to alternuting' currents, but non-continuous with respectto direct currents. The type of subfstation outfitshown one that I have select e l for the purpose of illustrating the invert t but it is to be rniderstood that I do not limit myself to the form of substation apparatus shown, for it will be seen as the description of the invention is proceeded with, that the operation of the system does not depend upon the particular substation outfit shown. Substation 1 is connected to the exchange in the form of the invention shown by means of metallic circuits, whose limbs 9 and 10 are connected with the line springs or talking contacts of spring jacks 11 and 12. A plurality of spring jacks is shown in multiple relation with each line, the lowermost spring ack 12 constituting the answering jack, while the remaining jacks, such as 11, constitute multiple jacks. The limbs 9 and 10 also terminate in contacts on the right and left armatures of cutoff relay 13, the limbs of each telephone line being normally connected by means of said armatures and the contacts normally engaged thereby with a line relay 14, the limb 9 being connected with the left hand winding and the limb 10 being connected with the right hand winding of. said relay, the other terminals of the windings of said relay being connected through grounded battery 15. Line relay 14 is actuated by the removal of the telephone receiver at substation 1 from its supporting switchhook by means of a circuit which may be traced as follows: from transmitter 3, through line 9, left hand armature and normal contact of cut-01f relay 13, left hand winding of line relay 14 to the live pole of grounded battery 15, through said battery to ground, through resistance 16, right hand winding of line relay 14, right hand normal contact and armature switch of cut-off relay 13, line 10, primary 7, switchhook 4, completing the circuit through transmitter 3. This actuation of line relay 14 causes its armature to close a circuit through line lamp or signal 17 which may be traced from ground, through said resistance 16, said armature and front contact of line relay 14, line lamp or signal 17, interrupter 18 and its brush through battery 15 to ground.

Interrupter 18 consists of a rotating metallic member with one or more insulating seg ments, there being a shunt circuit around said interrupter through resistance 19. Hence, the current passing through resistance 16, from line lamp or signal 17 is a variable one though not intermittent and the current from grounded battery 15 passing through the'same resistance to the described line circuit including primary 7 is also made variable thereby. This variable current sets up an alternating current in secondary 8 which is heard as an audible signal in the telephone receiver 2 which is in circuit with said secondary. It will be seen that if the circuit was open through limbs 9 and 10, there would be no path for the described variable current and hence no audible signal would he produced; and if the circuit was open through line lamp or signal 17, the current passing through resistance 16 would not be a variable one and no audible si nal would be produced. Therefore the production ofthe audible signal in the receiver 2 is an assurance to the party at substation 1. that the line wires are in working condition and that the line lamp or signal at the central exchange has been displayed.

Having observed the displayed line lamp or signal 17 of the calling substation, the operator inserts answering plug 20 into answering jack 12 corresponding to the calling substation. This action closes a circuit which may be traced as follows: From the grounded terminal of cut-off relay 13, through the winding of said relay, sleeve of answering jack 12, sleeve contact of answering plug 20, left hand winding of answering supervisory relay 21, winding of operators relay 22, armature and back contact of controlling relay 23 to the live pole of grounded battery 15, completing the circuit through the same. The actuation of cut-off relay 13, due to the current flowing through the traced circuit, breaks the circuit from substation 1 through line relay 14, and line lamp or signal 17 therefore resumes its normal condition due to the consequent disengagement of the armature of line relay 14 from its'contact. The actuation of operators relay 22 due to the current flowing through the same traced circuit causes its various armatures to be attracted.

The actuation of answering supervisory relay 21 due to the current flowing through the circuit just traced closes another circuit which. may be traced as follows: from ground, through battery 15, talking interrupter 24, front contact and armature of actuated answering supervisory relay 21, windingof answering relay 25, sleeve contact of answering plug 20, sleeve of answering jack 12, and winding of cut-off relay 13, completing the circuit to ground. The actuation of answering relay due to the current flowing through the circuit just traced causes its various armatures to be attracted.

A circuit may then be traced as follows: from ground, through repeating coil winding 26, uppermost armature and front contact of the two top ones of answering relay 25, ring contact of answering plug 20, ring contact spring of answering jack 12, limb 9, transmitter 3, switch-hook 4, primary 7, limb 10, tip spring of answering jack 12. tip contact of answering plug 20, right hand windingof answering supervisory relay 21 and the non-inductive resistance in multiple relation thereto, lowermost front contact and armature of the three bottom ones of answering relay 25, repeating coil winding 27, and grounded battery 15, completing the circuit to ground. The current thus alsubstation.

l t-races low-ed to flow through the right liand wind 111g of answering supervisory relay 21 as QI'OUHClCfl battery 15,. and receiver 2 is placed in inductive relation with windings 26 and 2:? of the repeating coil. party at-substatlonr 1 1s telephomcally connccted with the operator who has responded to the line signal, as the actuation of On eratoz'ls relay 2 connects the operators telephone receiver 28 to the line of the calling 1:. circuit tor this connection may be traced as follows: from ground through repeating. coil-winding'26, through the front contact and uppermost armatureof the two top ones 01; operators relay 22, secondary of operations induction coil S1, receiver condenser 32, 'bottoni armature and front left hand contact of" operators relay repeating coil winding 27 and grounded battery. 15, completing the circuit to ground. 1

lVhen cut-oiirelay 13 actuates, simultaneously with theactuation of answering su pervisory relay 2'1, and operators relay 22, the audible signal in receiver 2-at substation l ceased, as limbs QandlO were disconnected y from the variable current flowing throughres stance The cessation of this audible signal may be used as a notification to the party at substation 1 that an exchange operator is connected to his line and is ready to receive the number of the line he wishes to be connected to, as answering relay is actuated as soon as supervisory relay 21 is actuatech thereby completing a telephonic connection between the called party and the answering operator Theretorejthe usual verbal inquiry o itithe operator may be dispensed with. However, the operator may converse with the calling party, if desired or it necessary, by means otoperators transmitter and primary 341 of the operators induction coil.

Having been informed as to the number o'ttlie line that the calling party desires connection with, the A operator communicates with theB operator over a call wire (not shown). The B operator informs the A operator as to the number of the trunk taken ior use and then tests the called line. The busy test for the trunk line, shown in Fig. 3 is not made with the tip of the trunk plug as is usually the case, but is made by the use of apparatus illustrated in, ,2 wherein 245 represents a metallic thim'ble of any (four i cut form adapted to be worn on the end of one of the fingers of one or both oi the hands of the B operator. Previous to inserting trunk plug 25 i into a multiple the sleeve ot' said jack is touched by Therefore, the V Thimble 254 and iii? the same is :at .apots-n tia l abovethat of the earth (as is the case when: a busy line is tested), thecurrent flowing to ground through primary 2&6 which is connected ithimble 245 induces current in secondary 24:7 which is connected to the 13 operat0 "s telephone rc ceia-*er-= Secondary 2st? is pre' ,rabl-y iota high resistance S0239; notto impede the voice CHPL'QDTS from the A operators set which. pass iii-om the lines 245i and 2429 to said 1% -operator s receiver.

ill-t ter testing the calledtorline and having found it idle, the B operator inserts plug 254 into the multiple ack 211.

The A operator after receiving the numher of the assigned trunk from the B operator inserts calling plug into ji-aclr 255 thereby establishing acilrcuit traceable as follows: from grou-nd,through the sleeve of jack 255, sleeve contact of calling plug 35,, spring switch 38 and. back contact of calling relay 89, winding of ringing reh V 40, right and left hand contacts connected by the bottom armature of actuated operators relay22 and winding; 27 ot the repeating coil, completing. the circuit through grounded battery 15. Ringing relay it) is energized :in this circuit and its various .ZrllllittllIBS are attracted. Thewen-V gagement of the to-p armature of relay '40 with its two contacts closestwo circuits first, and then operates spring switches 42, 43-and 44. afterwards. The two bottom: armature'sof relay am not attracted until after the engagement of the top armature has taken place. The'circuits may be' traced as follows: first from the upper: terminal oi:

grounded battery, completing the circuit 7 through the circuit already traced sto ground atthe sleeve of jack- .255. The second circuit may be traced from the grounded terminal of magnetic clutch 416 of party line ringing key L7, releaselrey 48, the winding of said clutch, supervisory lamp 40, right hand- "trout contact. and top armature of ringing relay 40 and the left hand trout contact of the-same completing the circuit through .the circuit already traced through the upper winding of controlling relay 23 and ringing interrupter 451 The current thus allowed to flow through. said winding energizes relay 23 and its armature disengages its contact, opening the circuit through the winding otoperators relay 22 and left hand winding/of answering supe-ri visory relay :21. The consequent. deenergiza= tion of operators relay 22 releases its various armatures, removing the operators telephone set from telephonic connection with the calling substation and opening the energizing circuit of ringingrelay 40, which has been traced from the upper terminal of the winding of said relay through the two contacts of the bottom armature of operators relay 22. However, current still flows through the winding of ringing relay 10 to maintain the same actuated by way of the circuit traced through the upper winding of controlling relay lVith plug 35' inserted into jack'255 and with relay 40 operated, ringing current is now connected to the trunk circuit and relay 250 is operated over a path extending from ground through ringing machine 59, inter' rupters 89 and 78, normal contact and spring switch of key 51, alternate contact of the inner lower armature of relay 40, non-inductive resistance 63, normal contact and left spring switch of key 5%, normal contact and right spring switch of key 53, tips of plug 35 and jack 255, winding of relay 250, rings of jack 255and plug 35, left spring switch and normal contact of key 53, right spring switch and normal contact of key 54, winding 29 of the repeating coil, spring switch 44 and engaged contact of ringing relay 10, spring switch and normal contact of key 56, completing the circuit to ground. Since the return path for ringing current is through the winding 29 of the repeating coil and since the operators receiver 2 is inductively connected to the winding 29 of the re peating coil, the calling subscriber as well as the called subscriber, will receive an audible signal as long as ringing current is applied to the trunk circuit.

Relay 250, in operating, closes a circuit which may be traced as follows: from grounded battery 252, through the armature and front contact of trunk relay- 250,

trunk ringing supervisory lamp or signal 253 and sleeve contact of trunk plug 254,

completing the circuit to ground through the cut-off relay 210 when plug 254 is inserted in the multiple ack 211. The cutoff relay 210 and the trunk ringing supervisory lamp or signal 253 are both energized by the current flowing in this circuit.

If a single party station, such as station 500, is being called, ringing current for signaling said station will be impressed upon the called line over a circuit extending from tip spring of jack 255, spring switches 256 and 257 of relay 258, winding of relay 251, tip contacts of plug 254 and jack 211, the called substation hell or an nunciator, ring contacts of jack 211 and plug 254, spring switch 259, normal contact of relay 258 and ring spring of trunk jack 255, completing the circuit through the A board ringing devices over the path previ- '56, to ground.

ously described. Trunk supervisory relay 251 is energized by the current flowing in this circuit.

The cord circuit shown in Fig. 1, is provided with the necessary equipment for party line ringing. It will be understood that there may be a number of stations, such as 500, bridged across the line leading to the multiple jack 211. If a party line station is desired, the operator will depress a key in the cord circuit corresponding to the particular station of the party line desired. The paths for the ringing current when partly line ringing is employed, is fully described in the aforementioned application. Assuming, for example, that a party corresponding to the key 51 is desired, the operator will actuate key 51, whereupon a circuit for ringing current may be traced as follows: from ground, through ringing generator 59, interrupter (30, brush 61, interrupter 62, and its associated brush, upper alternate contacts of key 51, alternate contact and engaged uppermost armature of the two bottom ones'of ringing relay -10, noninductive resistance 53, normal contact and left spring of key 51, normal contact and right spring of key tip contact of calling plug 35 and thence over the path previously traced fromythe trunk circuit and the called substation loop, through the ring contact of plug 35, left hand spring 53 and its normal contact, right hand spring 54: and its normal contact, conductor 47, winding 29 of the repeating coil, spring switch 441 and front contact of relay 4L0, spring switches 55 and Trunk supervisory ringing key 251 is also energized by current flowing in this circuit.

when the called substation responds, the

high resistance winding of trunk relay 250 is shunted by the low resistance path formed at the called substation and its armature disengages its alternate contact and reengages its normal contact, thereby extinguishing trunk ringing supervisory lamp 253. The closing of the low resistance circuit causes the actuation of the calling relay and the deenergization of the ringing relay both located at the A board. Current from the repeating coil of the link connector now flows through the trunk circuit. As trunk supervisory relay 251 is in series with the substation circuit, it remains actuated and when the armature of trunk relay 250 reengages its normal contact, the circuit through the sleeve contact of trunk plug 254, which was opened by the disengagement of said armature from its alternate contact, is closed again but this time through the winding of necting relay 258, armature and front contact of trunk supervisory relay 251, normal contact and armature of trunk relay 250 and grounded battery 252, completing, the circuit 5 to ground. Due to the current flowing in this circuit, both the cut-off relay 210 and connecting relay 258 are actuated. The engagement of the top armature switch of re lay 25S and of spring 259 establishes a ground connection through the winding 260 of the repeating coil to the ring contact of the trunk .plug 254 previous to disengaging said spring switch from its normal contact, thereby breaking the connection from said ring contact to ground through the ring spring of trunk jack'2'55 and the repeating coil associated with the link connector at the A board. The engagement of the bottom armature of relay 258 with spring switch 257 establishes a connection from the live pole of grounded battery 252, through winding 26]: of the repeating coil to the tip contact oi the trunk plug,v previous to disengaging said spring switch from spring switch 1256, thereby opening the connection from the tip contact to the live pole of? the grounded battery through the tip spring of trunk jack 255 and the repeating coil associated with the link connectorat the A board.

In this manner, relay 251 is maintained actuated, though the source of energizing current has been changed from the repeating coilat the Aboard to the repeating coil associated with the trunk circuit. As the top and bottom armaturesotconnectingrelay connectcurrent of the same polarity to the tip and ring contacts. of trunk plug :95: as that connected thereto through the tip and ring springs of trunk ack 255, it is immaterial whether thearniatures engage their respective spring switches siinultaneouslyor not.

When the bottom armature oi connecting re ay 25S dis-engages spring switch 257 from spring switch 256, it engages the former with its alternate contact, and thereby bridges non-inductive resistance 262 across the inductive windingof trunk supervisory relay 251, allowing voice currents to pass said relay. At the same time, spring switch 256 has been allowed to engage its alternate contact, thereby closing acircuit which may be traced as follows: from the tip spring ct unk jack through said spring25 5 ant engaged alternatecontact, windin s 263 and 536% of the vrepeating coil, ring spring of trunk jack and thenceover the tal ing conductor of the calling link connector at the vb eting the circuit back U 7 1g. The high resistance of trunk relay 250 is, therefore, by the lower resistance and lower h hirnished by windi ing coil at the A board pass-through said windings263 and 26d. The trunk relay250 is not actuated by the current from said A board repeating coil due to the low resist ance shunt ilornied by the windings 263 and As the calledvsubslation is now directly connected to windings 260 and 2631 of the repeating coil, conversation can be carriedon through the connected substations. The engagement of theuppermost lot the two bottom armatures of connecting relay 258 with its right hand contact closes a circuit fi'omgrounded batteryQT, 2, through talking supervisory lamp or signal 265 which is thereby energized, and its engagement with its left hand contact short cir cuits the upper half of the winding of connecting relay 258,, the purpose of this shortcircuit being, as described in the aforementioned application, to furnish means for preyentiugan accidental or deliberate connec tion to a busy line.

This short circuit also furnishes current from grounded battery 252 to the lower half of. the winding of the connecting relay 258 independent of the armature of supervisory relay 251,,so that ;a momentary "disengagement of this armature does not deenergize the connecting relay.

When the telephone receiver of the called subscriber is replaced upon its switchho'ok, the circuit through supervisory relay is opened and, therefore, its armature switch reengages its contact which is connected to the sleeve contact of trunk plug 254;,

Therefore, the current from grounded battery 252 flowing through the uppermost one of the two bottom. armatures and the engaged. left hand contact of connecting relay 258 now has two paths offered to it, from the central. terminal of the winding of said relay toward both ends of the. same, and as these windings are in opposition to each other, the connecting relay is consequently deenergized, restoring the'other connections controlled by said relay to their normal condition. The circuit through the sleeve contact of trunk plug 254: beingiopenedfby the deenergization of the connecting relay 258,

the cut-oil relay 210 associated with the called line is deenergized and the control of the line relay 503, and the hue -lamp" or signal e01 of the called line isflrestored to the control of the called SUbSiJfl'ElOIL The disengagement of spring switch 256 'otconnecting relay 258 from its alternate contact when said relay 258 was deenergized, opened tl'iecircuit through the windings 2G3 and 264- of the repeating coil. Therefore,

the low resistance shuntnround the high resistance winding-of trunk relay f 250is removed and as the current, flowing through said windings, is notsuliicient toinaintaiu ac ted the calling supervisory relay associated with the link connector at the board which is connected to trunk jack said calling supervisory relay 50 is dc-energized and said link connector circuit opened.

If the telephone receiver of the calling station had been replaced before the called party answered, relay 21 would have deenergized due to the opening of its circuit at the calling substation. At this time answering relay 25 is actuated as hercinbefore described and a circuit is closed which has not been previously described. 1 This circuit may be traced as follows: from the live pole of grounded battery 15, through talking in terrupter 24, uppermost one of the three bottom armature switches and front contact of answering relay 25 to the center terminal of the winding of said relay through the upper portion of said winding, sleeve contact of answering plug 20, sleeve contact of answering jack 12 and winding of cut-off relay 13, completing the circuit to grounded battery 15. This circuit short circuits the lower half of the winding of answering relay 25 which received current from inter- .rupter 24, in the first place, through the alternate contact and armature of answering supervisory relay 21. lVith relay 21 deenergized as first described the current from interrupter 24 now has two paths leading from the central terminals of the winding of answering relay 25, one toward the upper terminal of said winding and thence to sleeve contact of plug and one towards the bottom terminal of the winding of relay and thence through the armature and normal contact of answering supervisory relay 21 to the sleeve of plug 20. As those two windings are opposed to each other, relay 25 becomes deenergized and its various armatures disengage their respective contacts. One of the objects in arranging for such a deenergi zation of relay 25 is on account of the sensitive action inherent insupervisory relays which are inserted in the talking circuits. A momentary disengagement of the armature of answering supervisory relay 21 from its alternate contact will not release answering relay 25 due to the shunt circuit around the armature, it being necessary for said armature switch to fall-all the way back and engage its normal contact before said relays can be affected. Current is thereby cut oil. from the tip, ring and sleeve contacts of answering plug 20 and therefore cut off relay 13 is deenergiaed, its armatures engaging their contacts thereby restoring line relay 14: and line lamp or signal 17 to the control of the apparatus at substation 1.

It will be seen therefore that it is immaterial whether answering plug 20 is removed or not from answering jack 12, as the three strands of the link connector are all open and from an operating standpoint there is no connection from the ack to thelinlr connector, As long as calling plug remains connected to the jack 255, controlling relay 23 remains actuated thereby maintaining the circuit open from out off relay 13 through the left hand winding of answering supervisory relay 21 and operators relay 22. The

restoration of the receiver to the switchhook at the calling substation previous to the response of the called substation also causes the deenergization of the ringing relay of the link connector engaged with the trunk jack 255. The deenergization of relay 4O opensthe circuit through the tip and ring springs of jack 255, thereby causing the deenergization of trunk relay 250 and trunk supervisory relay 251 and consequently, the circuit through trunk ringing supervisory lamp 253 and the sleeve contact of trunk plug 254: would also be opened. Therefore the cutoff relay 210 would have dcenergized and the line relay 503 and the line lamp 501 would be restored to the control of the called subscriber at substation 500. The line would test idle at any multiple ack associated therewith and the subscriber could initiate calls. v

The calling link connector at the A board, the trunk circuit and the called line are all released for further connections by the replacing of the telephone receiver at the called substation on its switchhoolr. Connections can be made from the released called substation regardless of the connection to a multiple jack associated with said line of the trunk plug of the released trunk circuit and the line will test idle at any multiple jack as the only connection from the tip and ring springs of said line, through said re leased trunk circuit, is through the winding of trunk supervisory relay 251 in series with the high resistance winding of relay 250. As this latter winding is not. only of high resistance but high impedance as well, the line lamp of the connected line is not energized thereby, nor are voice currents from the connected lino allowed to pass through said winding.

The embodiment of the invention shown in Fig. 3 is preferably intended for use where the outgoing trunk calls are handled by a single operator. lVhere more than one operator handles the outgoing calls, ringing current might be in'ipressed upon a line with which. a released trunk circuit was connected and said ringing current, passing through the ring and tip contacts of the released trunk circuit, would actuate relays 250 and 251. Therefore, when more than one operator handles the outgoing calls at the l) board, the embodiment of the system illustrated'in Fig. 4; is preferable.

In Fig. 1, trunk relay 266 corresponds to trunk relay 250 in Fig. 8, and it actuates as has been described in relation to said Fig. 3, excepting that the upper terminal of the wind ng o trunk relay 250 was con- 'tru n-k jaclc 255 and therepeating coil -of= the link connector at 'theA hoard while the upper tern'iinal -ot' trunk-relay 266, Fig. 4, 'is connected direct to ground at the B 1 board. This is done only if waiting connections are to he made through the trunk circuit. H the waiting connections are nsed-andthis ground connection- -W in-ade through the repeating coil attheA boa-rcht-hen the callin-g subscriber would receive-a false ringing audible signal through the suhstation -telephone receiver, *duetto ithe ringing current illon'ing" through trunk relay Q66 to main tuin its. actuation While the L trunk link; con- :necti-on --is.- iirthe Waiting condition.

On receiving; a call from "the "A- operator over -21 call Wirecircnit f (not -.sho-\v1'1), the B opcrater 'tests the called-for' line, such that shown at :the-=r ightof *Fig. 3, i by. on-

ringing supervisory lamp or signal 270,-

' which energizes the same. The insertion of ,pl-ugriQGS 'into the junk 4211 closes a circuit which may be traced ;as follows: flOHl ct iuclc2l 1, sleeve contact of calling-plug 268. resistance 271,to-p armature and norinalcontact (it-trunk controlling-relay 2'72, avinding of trunk riinringtrelay- 273, spring switch 27 and norn'ralcontact of: said relayyn'aitinginterruptcr-j275 and grmuidcd battery 269, completing the circuit "to gllouniil. The cut-oft relay-2'10 and .trunk wingingrelay 27 are bothene iZed-hvthe currentflowing throughth-is cir int whereupon :a circuit-is closed for theringingcnrrentfrolnithetipia11diingsprings "of trunk jack-2G7 which anzry hetraced as (follows: 1/

"l ronrthe-ring spring of jack' 267,-throiigh the 1 contact and engaged mi-ddle one oi? the three top armature 'SWlhChGSOftlflIlli relay Q73. ring Contact of trunk 13111;: 268, Substatioi'i call hell or annunciator,t p contact ()ii;1)'l,ti,i{268, r ght hand winding ottrunk s1 pervisory-relay- 27G, lowermost one of the two hottoinarinatures' o'ttrunk ringing relity 5273., its-engaged contact nnd'the'tip spring ottrunk j ack 267, cmn'pletin g the circuit to the ring: s i ringithroughfthe ringing "devices a==soc1ated "Wlill the link connector engaged The engagement 'fivith its contact otthe loiverlnost one ofthe three top armat-n-res of trunk ringing relay 1273 "closes asl 1nnt-ci1= cuit around resistancefifl which winayihe traced =as follows troin the a right 1 han d term=i n-al of resistance 2r 1, I inner 5 lower ydl'lll atn're and nornral-contact of trunk calling;

relay 277, arnmtu-re and front -contact o 'trnnk rin ging' rel zty 273, upper Winding-o trunkcontrolling relay 272, normal contact nn'd top armature switch of relay 272, completin-g the shnnt circnit to "the left hand 1 of -=resistance The current "flow/1n :tln'ongh-sa-i(lshunt circuit ism tilicient to-mwse the-actuation of trunk controlling re y, 272* and vi'l ien its top :arinaturc "disengagges its normal contact, the circuit is opened throuph :resistance Q'Zlnntlnll -the current "flowing through thesleeve contact of trunk itlug 2'68 and the Winding of trunk ringing-rcIay'Q73, now flows through the upper {\vin din of trunk controlling relayaQTQ. 1

The en-g a YL'IHGHU of the uppermo the two h, om a r-maturesotitrunh relay 27 8 with spring; switch Q'Mcon the lower terniinnh oI -the- Winding oteaid delay *clirect togronnded battery 269 belore thed-isengageinent o't said-spring switch fro'in its normal contactdisconnects saitl- *terininrl fronr'thehattery hysvary of Waiting ir-lterrupter 127-5. T'he engagement of the snoring switch 21 with: its alternatecontact short-circuits e p'art oh the -;winding; of said" relay, 1 the purpose I of which hasbeen her-e inhe't'ore described in- -connectionqvith Fig. 3.

hen the called substation responds, *tr-urilr relay 266 is shuntelc l by a low I resistand' therefore its arinetnne switch "disengages its 'alter-na'te contact, "thereby -extin-guishing the ringing supervisory sig naL-Q'ZO, un den- -g=aoes its normal contecn-ehsing a circuit =whi-ch may he traced as follows: itron'i groin-1d, throngh the cumflrclay 210' sleeve contact oftrunlc plug 268, which no of trunk calling" relay 277, left handWindingof trnnk i supervisory -r tru nk i ringn 1g --re.lay "273,1101111211 contact 7 armature of trunk relay 266 and i grounded battery 269, co1npleti ng the circ-uit to-g'ro-un-d. TrunkcaIlin-g relay "QTY-is ei-181, this circuit. Its euppermost [and middle anaemxtnresand its two bottom -ar 1natures engage their respective contacts before the lowern-iost ot-"the three top ones disengages its contact. The engagen'ient of the middle one: ofthe three top armatureswith its-contactconnects thering contact of trunk plug 268 to groundthrough Windi-ng QTS of the repeating coil and the --engagen:1ent ol the lowermost one of the two bottom arinhtnres *Wltllits two contacts 'bri 'clges"non-inductive resistance 2T9 eeross the right handwviirding =of trunk supervisory relay 276 and connects hoth to the live flooleof i grounded i battery "269' throu-gh WindingQSO-O f theirepeati-ng tone of rice pathns'h asbeen hereinhe' fore described,

ay 27 6, hppermost one and ot the three top armatnres to the control of the called substationcoil. The engagement with its Contact of the uppermost one of the-three top armatures of calling relay 277 closes the circuit from the tip and ring springs of trunk jack 267 through windings 281 and 282 of the repeating coil. Therefore, the two substations are telephonically connected and conversation can take place between them as soon as trunk ringing relay 273 is deenergized which takes place when the lowermost one of the three top armature switches of calling relay 277 disengages its contact, thereby opening the circuit through the winding of trunk ringing relay 273. The engagement with its left hand contact of the uppermost of the two bottom armature switches of calling relay 277 closed a circuit through talking supervisory lamp or signal 283 and grounded battery 269, the energization of said lamp or signal being the operators assurance that the called substation has responded. The engagement of said armature with its right hand contact had established a connection to the live pole of grounded battery 269 from the lowerterminalof the winding of trunk calling relay 277 previous to the breaking of the other connection to the same through the left hand winding of trunk supervisor-y relay 276, when the uppermost one of the three top armature switches of trunk ringing relay 273 disengaged its contact. Trunk calling relay 277 therefore, remains actuated.

hen the telephone receiver at" the called station is replaced upon its switchhook, trunk supervisory relay 276 is deenergized and the engagement of its armature with its normal contact short circuits the winding of calling relay 277 which is thereby deenergized, opening the circuit through the sleeve contact of trunk plug 268, deenergizing the cut off relay 210 and thereby restoring the line relay 503 and line signal 501 Therefore, the line will test idle at any multiple jack associated therewith At the same time the disengagement-from its contact of the uppermost one of the three top armatures of trunk calling relay 27 7, opens the circuit from the tip and ring spring of trunk plug 267 through windings '281 and 282 of the re aeatin coil thereb removin b 7 3 '3 the low resistance shunt from around the winding of trunk relay 266 and causing the calling supervisory relay associated with the link connector engaged with trunk plug 267 at the A board to be deenergized and said link connector circuit opened, as has been hereinbefore described in connection with Fig. 3.

\Vhen the busy test was made on the sleeve of the jack 211 of the called-for line, if the same had been busy, the sleeve would have been at a potential above'that of the earth and current would have flowed through the tipcontact of trunk plug 268, non-inductive resistance 279, bottom arma- .ture switch and normal contact of trunk controlling relay 272 and special primary 28 i of the operatorsinduction coil to ground. This would have caused a signal to be heard in the-telephone receiver285 on account of its. connection to the secondary winding 286 .of the inductlon coil.

been distinctiveto waiting interrupter 275.

The circuit for the current producing this signal may be traced as follows: from ground, through'the primary 28 1, back contact and lower armature of relay 272, resistancee-leme-nt 279, tip contact of calling plug 268, sleeve of the multiple jack of the tested line, sleeve of the multiple jack associated with said line to which is connected the link connector impressing ringing current on said line, sleeve contact of the calling plug such as 268 associated with said link connector, resistance 271, upper armature and back contact of relay 272, winding of relay 273, spring 274 and normal contact through the interrupter 275 to ground through the battery 269. If said link connector had been in aringing or talking condition, the signal in said receiver would have been in the nature of a click, as constant current from grounded battery 269 would flow through the primary winding 28% of the operators induction coil.

lVhen a connection is made to a busy line, trunk ringing relay 273 is prevented from fully actuating in the same manner as has been'described in my aforementioned patent in relation to ringing relay 40 (Fig. 1).

However, the uppermost and lowermost ones of the three top armatures of relay 273 engage their respective contacts, though all the other armatures do not engage their re spcctive contacts. Trunk controlling relay 272- is energized therefore. by the current flowing through its upper winding. and the disengagement of its armature switch from its contact prevents trunk ringing relay 273 from being energized again should the tele phone'receiver at the calling substation be replaced upon its switchhook previous to the response of the called substation.

Trunk controlling relay'272 has a lower locking winding which maintains said relay actuated as long as trunk plug 268 is inserted in a jack, its function and mode of operation being the same as that described in relation to controlling relay 23, Fig. 1.

In the eventthat the calling party replaces the receiver upon its switclihook previous tot-he response of a called party, the

consequent engagement of the armature switch of trunlr relay 266 with its normal contact would close the already described circuit through the engaged contact and uppermost one of the three top arniatures of trunk ringing relay 273 and the left hand winding; of trunk supervisory relay 276 and where a trunk calling relay 2?? was consequently energized. the disengagement of the lowermost one of the threetop armatures from its contact will deenergize relay 2T3, thereby deenergizing the left hand winding oi? trunk supervisory relay 27o, and the right hand winding of said relay would not be energized, (due to thefact that there is no closed circuit for direct current at the called suibstation which has not responded). its armature switch would engage its normal contact. thereby short circuiting the winding); of trunk calling relay 27? ant deenergizing the same. The same procedure would take plac it the telephone receiver at the calling substation was replaced on its switchhool: when ringing; current was being impressed on the line. In both cases the called-torline is automatically restored to its normal idle condition.

The completion of the call when awaiting connection is made and the busy. line is released, is the same as that described in relation to Fig. 1 in my aforesaid application. The engagement with its contact oi. the middie one of the three top arniatures of trunk ringing relay 273 ant. the engagement with. its contact ot' the lowermost one of the two bottom armatures of said relay allows ringiug' current from the A board to be im- )re:=;sed upon the called for line and as the return path to ground for said current is throuch the grounded winding of the repeating coil associated with the link connector en uged with trunk ack 26?, the calling p y receives an audible signal in the substation. telephone receiver which as sures him that the substation call bell otthe line he is waiting for has been released from its busy condition and is being rung upon. For party line ringing the proper ringing lzev is depressed or manipulated by the operator at the A board and ringing; current then sent out in the manner fully described in the aforesaid application.

In Figs. 5 and 6 I have illustrated more complete embodiment of the adaptation of the system to trunk line work. In these embodiz..-.ents the ringing current is tarnished from either the A. or boards. In Fig. 5 l have shown the ringing current as being furnished from the B board and in Fig. 6 I have shown the connections to be changed from the showing-in Fig. 5 it the ringing current is furnished from the A board.

As many features shown in Fig.5 have already been amply described, mention will be made only of those features which differ from those illustrated. in the preceding igures.

When the A operator inserts the calling plug in the trunk jack 289 a circuit for the ringing current is closed which may be traced as follows: from the tip spring of trunk jack 289, through the lower winding of trunk relay 290 (which is of low resistance), spring switch 291 and normal contact of trunk calling relay 292 and upper Winding of trunk relay 290 (which is of high resist.- ance). completing the circuit to ground and therefore to the grounded terminal of the ringing generator associated with the A board. Duringthe interyal between the inipression of alternating current .on this circuit, the intermittent, direct current from the battery interrupter 91 in Fig. 1 is impressed upon the same circuit and trunk re? lay 290 is actuated by both of said currents as are the trunk relays illustrated in the preceding figures. The actuation of trunk relay 290 which is'sirnilar to the described trunk relays illustrated in the preceding figures, closes a circuit from grounded battery 293, through trunl; ringing supervisory lamp orsignal 29st,. Thisla p or signal is energized by the current flowing through this circuit, its energization always indicating that the called line has not responded.

. The busy tests are made in the sa ne 'inanigier as described in relation to Fig. 4.

When the trunk plug 295 is inserted in a multiple jack suchas 211, a circuit is closed which may be traced as follows: from ground. through the cut-oil relay 2101 sleeve contact of jack 211 sleeve of trtuik plug 295, resistance 296, normal contact and upper armature of trunk controlling; relay 29?, winding of trunk ringingrelay 298, spring switch 299 andnor nal contact of said relay" waiting interrupter 300 and grounded battery 293 coni1i leting the circuit togronnd.

If the connection has been made to a bus line, trunk ringing relay 298 is only partially energizedin the manner that has been heretofore described. The lowermost one of the two top armature switches of relay 298 engages its two con acts the engah'ei nent; with its right hand contact energizing; trunk controlling relay 297 which remains energized as long as trunk plug 295 is engaged with a jack on account of't he current flow ing in its lower winding.

If the connection has been made to an idle line, trunk ringing; relay 298 is fully energized and all its respective arnzature and spring switches engage or (ii. their respective contacts.

Previous to the response of the called substation, whether the connection be a waiting one or not, if the calling par y replaces his receiver upon its switchhook, trunk relay 290 is deenergized and its armature switch engages its normal contact. As said armature switch is connected to grounded battery 293 and its normal contact connected to the left hand contact of the lowermost one of the two top armature switches of trunk ringing relay 298, which is engaged with its armature switch, the upper winding of trunk controlling relay 297 and the winding of trunk ringing relay 298 are short circuited and trunk ringing relay 298 is therefore deenergized, the lowermost one of its two top armature switches disengage its right hand contact first and then its left back contact thereby removing the short circuit made when the armature switch of trunk relay 290 engages its normal contact. As said disengagement with the right hand contact has already opened the circuit through the winding of said relay and as controlling relay 297 remains energized due to the current flowing in its lower Winding, trunk ringing relay 298 cannot again be energized until calling plug 295 is removed from the jack, thereby deenergizing the trunk controlling relay 297. The deenergization of the trunk ringing relay 298 restores the called for line to its normally idle condition, allowing the same to test idle at all its associated multiple contacts and restoring the control of the line signal to the substation associated with said line.

. l/Vhen trunk ringing relay 298 is fully energized ringing current is impressed upon the line around the Winding of trunk supervisory relay 301 from constant ringing interrupter 302 and intermittent battery current is impressed on the line from said winding through battery interrupter 303 in the same way as hereinbefore described in relation to Fig. 1. No interrupter to produce periodic ringing is shown in Fig. 5, though one may be used as also may be used any of the various forms of party line ringing illustrated in Fig. 1. V

The return path for the ringing current to the grounded terminal of alternating current ringing generator 304 is through the ring contact of trunk plug 295, uppermost one and engaged contact of the two top armatures of trunk ringing relay 298, ring spring of trunk jack 289 at the A board and thence to ground through the repeating coil associated with the link connector engaged with said trunk jack. As said contact and armature of trunk ringing relay 298 are not engaged when waiting connection is made, the calling party does not receive an audible ringing signal until the call bell has actually I been rung.

hen the called party responds trunk supervisory relay 301 actuates as heretofore described in the previous cases. The engagement of its armature with its alternate contact closes a circuit through trunk calling relay 292 which may be traced as follows: from ground, through the cut-off relay and sleeve contact of trunk plug 295, alternate contact and engaged armature of trunk supervisory relay 301, winding of trunk calling relay 292 and grounded battery 293, completing the circuit to ground.

Trunk calling relay 292 is shown diagrammatically in Fig. 5 as performing its functions in a certain sequence; while this illustrated and described sequence of operative functions is not obligatory, I pre fer its form'on account of the absolute assurance it offers that the change from the described ringing connections to the described talking connections will always be carried out in the proper way. As said sequence of operations does not rely on any adjusting means frequent use of the relay and the consequent wearing away of its contacts and moving members cannot effect said sequence. Also, battery commutator 303 impresses an intermittent direct current on the circuit including the winding of di rect supervisory relay 301; while this relay can readily be made to maintain its armature switch engaged over its alternate contact, without vibrating. when its winding is energized by this intermittent direct current on account of the great rapidity of the pulsation of said current, to do so entails a comparatively large core for the electromagnet or a comparatively large armature or both. As this destroys to a great extent the rapidity of action of said relay which is most desirable in a supervisory relay, I prefer to use a means similar to the one illustrated in Fig. 5 as in that case trunk supervisory relay 301 may be the same class of sensitive relay now used for supervisory purposes and which is well known in the art. It will be readily understood that calling relay 39 illustrated in Fig. 1 can be similarly arranged as its connections are similar in character.

When trunk supervisory relay 301 actu ates, its armature switch may or may not rapidly engage and disengage its alternate contact, due to the intermittent current from battery interrupter 303 flowing through its winding, it being immaterial as far as the actuation of trunk calling relay 292 is concerned, whether such vibration takes place or not. Trunk calling relay 292 is so arranged that its bottom armature switch moves with the greatest freedom,

without necessarily incurring any move.

ment of the other armature switch of the various spring switches. Therefore, if the and said spring switch 305 connected to its alternate contact, a bridged circuit is formed around the vibrating armature switch of trunk supervisory relay 301 and, therefore the winding of trunk calling relay 292 receives a constant current instead of an intermittent one. This constant current cause, its top armature switch to engage spring switch 291 and then to disengage the same from its normal contact, and its bottom armature switch to continue its actuation. The niovementot spring switch 305 causes the lowermost one of the various spring; switches to close a circuit from grounded battery .293, through talking supervisory lamp or signal 306, the energization of the latter always indicating to the operator thatthe trunk link connector is being used for conversationalpurposes. The operation of the remaining spring: switches takes place in sequence as follows: first, the normal contact of the middle one of the three bottom armature switches of trunk ringing relay 298 is connected to the live pole of ground-- ed battery 293 through the winding 30'? of the repeating coil; second, the ring contact of trunk plug; 295 is connected to ground through Winding 308 of the repeating coil; third and last, spring switch 309 disengages its contact. The first and second described actions may be reversed or so arranged as to be performed simultane ously, the only purpose in the sequence of operations being to insure the making of the connections to windings 307 and 308 of the repeating coil previous to the disen gagement of spring switch 309 from its contact.

The described actuation of the top armature switch of trunk calling relay 292 has changed the circuit connections at the B board between the tip and ring limbs of the trunk line, said circuit may now be traced as follows: from the tip spring of trunk jack 289, lower winding of trunk relay 290, sprint-2' switch 291 oi trunk calling relay 292 and engaged armature switch and windings 5310 and 311 at the repeating" coil, completing the circuit through the ring spring of trunk jack 289 and the link connector apparatus associated therewith.

The upper high resistance winding of trunk relay 290 is disconnected troin said tip spring wl'ien said ar iature discngages spring; switch 291 il'liil'fir tion of the series windings 310 and 311 of the repeating coil to said tip and ri springs turnishes a low resistance pt Lll which causes the actuation ot the ca ling supervisor-w relay'and calling relays associated with the link connector at the A board which connected to said springs.

The disengagement of spring switch 309 ottrunk calling relay 292- iroin'its contact, opens the circuit through the upper winding oi trunk controlling relay i297 and trunk ringing relay 298, the tormer remaining encrgized'due to the current flow-inn in its an and. the '(YOAHQC- lower winding and the latter being deenergized. The return to normal condition of the two bottom armature switches of the latter relay disconnects the ringing current from 8 the tip contact of trunk pln, j and connects said contact-to winding 30? ot' the repeating; coilthrough'the spring switch contact already made by the actuation ottlie trunk calling relay 292. The connection from the winding of trunk supervisory relay 301 has been changed in. the same man neras hereinbefore described. thelower low resistance winding ot'trnnk relay 290 is bridged by condenser 312 and as the tip and ring vsprings of trunk jack 289 are connected through windings 310 and 311 of the repeating coil and the tip and ring contacts oi" trunk plug 295 are connected to windings 307 and 308 of the same, conversation can take-place between the calling and called subscribers.

When the called substation telephone receiver is replaced upon its switchhook, the winding of trunk calling relay 292 is short circuited by'the engagement of the arma-v ture-of trunk supervisory relay 301 with its normal contact, due to the deenergization of said relay. Theconsequent deenerg'ization 01" said trunk calling relay and the disengagement of its top armature from spring switch 291, connects the high resistance upper winding: of trunk relay 290 to the ring" spring of trunk jack 289 and disconnects the lowresistance windings 310 and 311 of the repeating coil from the same. Consequently, the calling si-ipervisery relay ot the link connector engaged withsaid jacl: at the A board is d-eenergized and the, link connector andtrunlz line release in the hereinbef-ore described manner. vThe called line is restored to its normal idle condition in the same manner as been hereinbefore described.

' ing actuated the operators induct on coil and the disengagement of the top arn'iature switch prcvents trunk ringing relay 298 from again beas has been hereinbetore described.

Fig. as described and illustrated may be arranged for the ringing apparatus to be located at the exchange wherein the B board is installed and may then be inodilied according to the showing in Fig. 6 and consequently, if the party line ringing was used (the trunk circuit being'modiiied accordingly as illustrated in Fig. 1), the B operator would have to manipulate party line keys. If it, therefore, is desired to use the trunk circuit of Fig. 5, but with A board control of the ringing then the desired result can be accomplished by merely changing the connection from the alternate contact of the middle one 01" the three bottom armatures of trunk ringing relay 298 as shown in Fig. 0 by line 31*; and the connection from the lowermost one of said armature switches as shown in Fig. 6 by line 315 to a connection to battery interrupter 91 as illustrated in this figure as 'well as in Fig. 1 where it is located at the telephone exchange where the A board is installed. lVhen these changes are made whatever class of ringing current was impressed upon the tip and ring springs of trunk jack 289 by the A operator would operate the call bell at the desired substation, the ringing current passing from said tip spring to said alternate contact of trunk ringing relay 298 instead of from ringing interrupter 302. The change of the other connection from intermediate armature 303 to a connection to the same interrupter at the other exchange is made because it is essential for the operation of the disclosed system of automatic ringing that the intermittent direct current be impressed upon the called substation line through the winding of trunk supervisory relay 301 in exact synchronism with the intervals between the impression of the alternating or pulsating current as the case may be, from the in terrupters connected direct to the ringing generator. It the ringing generator interrupter was located at one exchange and the battery interrupter was located at the other, such synchronism would be difficult to obtain, though it might be accomplished if desired. Therefore, as it is much simpler and only requires one Wire between two exchanges, I prefer the change as indicated by line 315, as absolute synchronism is ob tained thereby between the functions of the alternating and direct current interrupters, inasmuch as the same are mounted on the same shaft and are so connected as toresolve uniformly. As the circuit for the intermittent direct current is closed through the winding of trunk supervisory relay 301 for a very brief interval representing the time needed to energize said relay lirst, then energize trunk calling relay and then deenergize trunk ringing relay 298, the amount of current that will fiow through line 315 at any one time is exceedingly small as inpractice but few trunk supervisory relays will actuate it precisely the same time. Therefore, said line which connects the two exchanges can be common to all the trunk circuits at the B board which originate at the same exchange and need not be of large current carrying capacity, not alone tor the reason detailed above, but on account oi the fact that trunk supervisory relay 301 actuates with a small amount of current, due to the fact that the non-inductive resistance 316 is not bridged across its winding until after trunk calling relay 292 has fully actuated.

i i hat is claimed is:

1. In a telephone system, a calling line, a called line, stations for each of said lines, an operators cord circuitand a trunk circuit for interconnecting said lines, said trunk circuit comprising in part a common path for talking and ringing purposes and in part separate paths for each of these two purposes, means for applying ringing current to the called line over the two parts of the ringing path, and means responsive to the restoration oiithe calling line for disassociating the ringing current from the called line and for establishing an electrical condition in thetrunk circuit and the called line indicating a non-busy condition and without disabling the ringing paths to permit a recall of said called line over said ringing paths.

2. The combination in a telephone system of line wires leading from a central oliice to subscribers stations, a cord circuit and a trunk circuit for establishing a connection between a calling and a called one of said stations, a trunk circuit having a portion common for both ringing and telephone conversation and another portion divided into two parts, one for ringing and the other for telephone conversation, a source of ringing current, means for connecting current from said source to the called line over the ringing paths, means controlled over a part of the trunk circuit by one of the subscribers and over a part of the cord circuit and the trunk circuit by another of the subscribers for disconnecting the ringing current from the called line, and means actuated by the calling subscriber for establishing an electrical condition in the trunk circuit and the called line indicating a non-busy condition without disabling the ringing paths to permit a recall of said called line over said ringing paths. v

3. A telephone exchange system including telephone lines extending from substations having calling signal apparatus to an exchange, an answering switchboard and a trunking switchboard means for connecting said switchboards comprising a cord circuit at said answering switchboard, a source of si 'naling current associated with said cord circuit at said answering switchboard, a trunk circuit at said trunking switchboard to connect to a called substation, means to impress signaling current from said source over said cord circuit and trunk circuit upon the line of said substation to actuate said calling signal apparatus, and means under control of apparatus at a calling substation connected to said cord circuit at said answering switchboard to discontinue said impression of signaling current from the cord circuit but maintaining the trunk circuit portion of the ringing current path complete.

4:. In a telephone system, a calling subscribers line, a called subscribers line, an operators cord circuit and a trunk circuit for manually connecting said lines means in the cord circuit and trunk circuit operating to apply a busy potential on the called subcribers line when said lines are connected, means controlled by the calling subscribers line for removing said busy potential without-taking down the manual connection, means for signaling the called sub' 35 the signal and for maintaining said path complete after the busy condition has been removed and means for preventing the reand for maintaining the signaling path complete if a called subscriber has not answered when the busy condition is removed.

5. In a telephone system, a calling subscribers line, a called subscribers line, a cord circuit and a trunk circuit for connecting these lines, said trunk circuit having two paths, one for signaling purposes and another for telephone conversation, means for applying ringing current automatically to the called subscribers line over the sig nal path established when said lines are first connected, means for establishing a busy potential on the called subscribers line when said lines are connected, means for disabling said busy potential and simultaneously iemoving the ringing current from the line without establishing the path for telephone conversation if the called subscribor has not answered the call, means for establishing said path for telephone conversation and removing the ringing current when the called subscribed answers and means for disabling said busy potential and maintaining the path for the telephone conversation through the trunk circuit complete after the called subscriber has answered the call.

In witness whereof, I hereunto subscribe my name this 31st day of January A. D., 

